1. Field of Invention
The invention relates to a scroll type compressor, and more particularly, to a scroll type compressor with a variable displacement mechanism.
2. Description of the Prior Art
A compressor for use in an automotive air conditioning system is driven generally by the automobile engine through an electromagnetic clutch. If the compressor is not provided with a variable displacement mechanism, when the engine rotates at a high rate the compressor will be driven at a high rate as well and the operating capacity of the compressor may be larger than necessary. Therefore, in order to ensure proper functioning of the compressor, the electromagnetic clutch must be turned on and off frequently. This frequent control of the electromagnetic clutch causes a large change in the load on the engine, reducing the speed and acceleration performance of the automobile.
Scroll-type compressors with variable displacement mechanisms for varying the compression ratio are well-known in the art. A scroll type compressor with a variable displacement mechanism is disclosed in U.S. Pat. No. 4,744,733 to Terauchi et al., incorporated by reference. With reference to FIG. 1, a scroll-type compressor with a variable displacement mechanism according to one embodiment of the '733 patent is disclosed. The scroll type compressor includes compressor housing 10 having front end plate 11 and cup-shaped casing 12 which is attached to an end surface of front end plate 11. Opening 111 is formed in the center of front end plate 11 and drive shaft 13 is disposed in opening 111. Annular projection 112 is formed on a rear surface of front end plate 11. Annular projection 112 is disposed within opening 121 of cup-shaped casing 12 and is concentric with opening 111. An outer peripheral surface of projection 112 extends along an inner wall of the opening of cup-shaped casing 12. Opening 121 of cup-shaped casing 12 is covered by front end plate 11. O-ring 14 is placed between the outer peripheral surface of annular projection 112 and the inner wall of opening 121 of cup shaped casing 12 to seal the mating surfaces of front end plate 11 and cup-shaped casing 12.
Annular sleeve 16 projects from the front end surface of front end plate 11 surrounding drive shaft 13, and defining a shaft seal cavity. Sleeve 16 is formed separately from front end plate 11. Sleeve 16 is fixed to the front end surface of front end plate 11 by screws (not shown). Alternatively, sleeve 16 may be formed integrally with front end plate 11.
Drive shaft 13 is rotatably supported by sleeve 16 through bearing 17 located within the front end of sleeve 16. Disk-shaped rotor 131 is located at the inner end of drive shaft 13 and is rotatably supported by front end plate 11 through bearing 15 located within opening 111 of front end plate 11. Shaft seal assembly 18 is coupled to drive shaft 13 within the shaft seal cavity of sleeve 16.
In operation, drive shaft 13 is driven by an external power source, for example, the engine of an automobile, through a rotation transmitting device such as magnetic clutch 20 including pulley 201, magnetic coil 202, and armature plate 203. Pulley 201 is rotatably supported by ball bearing 19 carried on the outer surface of sleeve 16. Electromagnetic coil 202 is fixed about the outer surface of sleeve 16 by a support plate. Armature plate 203 is elastically supported on the outer end of drive shaft 13.
Fixed scroll 21, orbiting scroll 22, a driving mechanism for orbiting scroll 22, and rotation preventing thrust bearing mechanism 24 for orbiting scroll 22 are disposed in the interior of housing 10. Fixed scroll 21 includes circular end plate 211 and spiral element 212 extending from one end surface of circular end plate 211. Fixed scroll 21 is fixed within the inner chamber of cup-shaped casing 12 by screws 25 screwed into end plate 211 from the outside of cup-shaped casing 12. Circular end plate 211 of fixed scroll 21 partitions the inner chamber of cup-shaped casing 12 into two chambers, front chamber 27 including suction chamber 271 and rear chamber 28. Spiral element 212 is located within front chamber 27.
Partition wall 122 axially projects from the inner end surface of cup-shaped casing 112. The axial end surface of partition wall 122 contacts the axial end surface of circular end plate 211. Partition wall 122 divides rear chamber 28 into discharge chamber 281 formed at the center portion of rear chamber 28, and peripherally located intermediate pressure chamber 282. Gasket 26 may be disposed between the peripheral end surface of partition wall 122 and circular end plate 211 to secure the surfaces. Additional interior walls of casing 12 form communication chamber 283 and cylinder 362. Chamber 283 is linked to cylinder 361 through communicating hole 361a, and cylinder 361 is liked to intermediate chamber 282 through communicating hole 361b. Control mechanism 36 is disposed in cylinder 361.
Orbiting scroll 22 is located in front chamber 27 and includes circular end plate 221 and spiral element 222 extending from one end surface of circular end plate 221. Spiral element 222 of orbiting scroll 22 and spiral element 212 of fixed scroll 21 interfit at an angular offset of 180.degree. and a predetermined radial offset, forming sealed spaces between spiral elements 212 and 222. Orbiting scroll 22 is rotatably supported by bushing 23 through radial needle bearing 231. Bushing 23 is eccentrically connected to the inner end of disk-shaped rotor 131.
When orbiting scroll 22 orbits, rotation is prevented by rotation preventing/thrust bearing mechanism 24 located between the inner end surface of front end plate 11 and circular end plate 221 of orbiting scroll 22. Rotation preventing/thrust bearing mechanism 24 includes fixed ring 241, fixed race 242, orbiting ring 243, orbiting race 244, and balls 245. Fixed ring 241 is attached to the inner end surface of front end plate 11 through fixed race 242 and has a plurality of circular holes 241a. Orbiting ring 243 is attached to the outer surface of circular end plate 221 of orbiting scroll 22 through orbiting race 244 and has a plurality of circular holes 243a. Each ball 245 is placed between one hole 241a of fixed ring 241 and one hole 243a of orbiting ring 243, and moves along the edges of the holes, allowing orbital motion of orbiting scroll 22 but preventing rotation. Also, the axial thrust load from orbiting scroll 22 is supported on front end plate 11 through balls 245.
Compressor housing 10 is provided with inlet port 31 and outlet port 32 for connecting the compressor to an external refrigeration circuit. Refrigeration fluid from the external circuit is introduced into suction chamber 271 through inlet port 31 and flows into the sealed spaces formed between spiral elements 212 and 222 when the spaces between the spiral elements sequentially open and close during the orbital motion of orbiting scroll 22. When the spaces are open, fluid to be compressed flows into these spaces but no compression occurs. When the spaces are closed, no additional fluid flows into the spaces and compression begins. Since the location of the outer terminal ends of spiral elements 212 and 222 is at final involute angle, the location of the spaces is directly related to the final involute angle. Refrigeration fluid in the sealed spaces is moved radially inwardly and is compressed by the orbital motion of orbiting scroll 22. Compressed refrigeration fluid at center sealed space 272 is discharged to discharge chamber 281 through discharge port 213, which is formed at the center of circular end plate 211. Discharge port 213 is covered by conventional flap valve 33 which allows communication in only one direction from sealed space 272 to discharge chamber 281.
Referring to FIGS. 1 and 2, a pair of holes 214, 215 are formed in end plate 211 of fixed scroll 21 and are symmetrically placed so that in operation an axial end surface of spiral element 222 of orbiting scroll 22 simultaneously crosses over both holes 214, 215. Holes 214 and 215 link the sealed spaces with intermediate pressure chamber 282. Hole 214 is placed at a position defined by involute angle .phi. (not shown) and opens along the inner side wall of spiral element 212. Hole 215 is placed at a position defined by involute angle (.phi..pi.) (not shown) and opens along the outer side wall of spiral element 212. A valve member having valve plates 341, 342 is attached by fasteners 351, 352 to the end surface of end plate 211, covering holes 214, 215, respectively. Each valve plate 341, 342 is made of a spring type material so that the bias of each valve plate 341, 342 pushes it against the opening of holes 214, 215 to close each hole.
Communicating channel 29 is formed through an outer side portion of end plate 211 of fixed scroll 21 near the terminal end of spiral element 212. Communicating channel 29 links suction chamber 271 of front chamber 27 with intermediate pressure chamber 282 through communication chamber 283 and cylinder 361. Control mechanism 36 controls fluid communication between communication chamber 283 and intermediate pressure chamber 282 through communication holes 361a and 361b in cylinder 361. Control mechanism 36 includes I-shaped piston 362 slidably disposed within cylinder 361, coil spring 363 disposed between the lower end portion of piston 362 and the bottom portion of cylinder 361 to support piston 362, and magnetic valve 364. Lower projection 367 extends from piston 362 and fits within hole 361b when piston 362 is in its lower position. First opening 361a is formed on a side surface of cylinder 361 and links cylinder 361 with communication chamber 283. Second opening 361b is formed on the bottom portion of cylinder 361 and links cylinder 361 with intermediate pressure chamber 282. The upper portion of cylinder 361 is covered by plate 365 which includes aperture 366 at its center. Cylinder 361 is linked with discharge chamber 281 through capillary tube 368 and aperture 366. Fluid communication between cylinder 361 and discharge chamber 281 is controlled by magnetic valve 364 disposed on housing 10. Piston ring 362c is located around an upper peripheral surface portion of piston 362 to prevent leakage of high pressure fluid between the space of cylinder 361 exterior to piston 362 and the space within piston 362.
When orbiting scroll 22 orbits due to rotation of drive shaft 13, refrigeration fluid flows into suction chamber 271 through inlet port 31 and then flows into sealed spaces (fluid pockets) defined between spiral elements 212 and 222. As the refrigeration fluid in the sealed spaces moves toward the center of spiral elements 212 and 222 the volume is reduced and it is compressed. The fluid is then discharged through discharge port 213 to discharge chamber 281.
When electromagnetic valve 364 is not energized, there is no communication between discharge chamber 281 and cylinder 361. Piston 362 is urged upwardly by the recoil strength of spring 363, and bottom portion 362b of piston 362 is located upwardly of first opening 361a. Intermediate pressure chamber 282 is linked to communication chamber 283 through cylinder 361 and openings 361a and 361b. Therefore, intermediate pressure chamber 282 maintains the suction pressure and some refrigeration fluid in the fluid pockets flows back into suction chamber 271 through intermediate pressure chamber 282 and communication chamber 283 via holes 214 and 215. Therefore, since the compression phase of the compressor is delayed until after the spiral element passes over and seals holes 214 and 215 isolating suction chamber 271 from the fluid pockets, the compression ratio of the compressor is reduced.
When electromagnetic valve 364 is energized, compressed fluid in discharge chamber 281 flows into cylinder 361 through conduct 368. Since the recoil strength of spring 363 is selected to be less than the force provided by the compressed fluid, piston 362 is pushed downwardly by the compressed fluid. Second hole 361b which links cylinder 361 with intermediate pressure chamber 282 is closed by piston 362, preventing communication between communication chamber 283 and intermediate pressure chamber 282. Therefore, the pressure in intermediate pressure chamber 282 gradually increases due to fluid passage from the fluid pockets through holes 214 and 215. The passage of compressed fluid continues until the pressure in intermediate pressure chamber 282 is equal to the pressure in the fluid pockets. When pressure equalization occurs, holes 214 and 215 are closed by the spring tension of valve plates 341 and 342. Compression then occurs normally and the displacement volume of the sealed fluid pockets is the same as the displacement volume when the terminal end of each spiral element 212, 222 first contacts circular end plates 211, 221.
Referring to FIG. 3, a second embodiment of the control mechanism of the prior art compressor of FIG. 1 is shown. Control mechanism 40 includes piston 402 slidably disposed in cylinder 401, bellows element 403, and spring 404. Piston 402 includes openings 402a and 402b and is pushed upwardly by spring 404 disposed between the bottom portion of cylinder 401 and a lower end surface 407 of piston 402. Surface 407 closes opening 361b when piston 402 is lowered against spring 404. Bellows element 403 includes valve element 403a, and bellows 403b disposed with piston 402. Valve element 403a extends exterior of the top of piston 402 through opening 402a formed in the upper portion of piston 402. The interior of piston 402 is linked to cylinder 401 through hole 402b. Cylinder 401 is linked to discharge chamber 281 through upper chamber 405, conduit 368 and capillary tube 406.
Since the interior of piston 402 is linked to communication chamber 283 through opening 402b, cylinder 401, and opening 361a, if the pressure in communication chamber 283 is less than the pressure of the fluid enclosed in bellows 403b, bellow 403b expands. Valve element 403a opens opening 402a of piston 402, and a small amount of compressed fluid which is supplied to the top space of cylinder 401 from discharge chamber 281 flows into communication chamber 283 through piston 402 and cylinder 401. In this situation piston 402 is pushed upwardly by the recoil strength of spring 404, and communication chamber 283 is linked to intermediate pressure chamber 282 linking suction chamber 271 to the fluid pockets. Therefore, the compression ratio is decreased.
If the pressure of the fluid in communication chamber 283 is greater than the pressure of the fluid in bellows 403b, bellows 403b contracts and opening 402a is closed by valve element 403a. In this situation, a small amount of compressed fluid flows from discharge chamber 281 into the top space of cylinder 401, and piston 402 is pushed downwardly against the recoil strength of spring 404. Opening 361b is closed by piston 402, suction chamber 271 is isolated from intermediate pressure chamber 282 and the compression ratio is increased.
Referring to FIGS. 4 and 5, a third embodiment of the control mechanism of the prior art compressor is shown. Magnetic clutch 20 and its associated elements are not shown in FIG. 4. Elements of FIG. 5 which are similar to those of FIG. 3 have been given like reference numerals. Needle-ball type valve 41 is connected to bellows 403b via connecting rod 403c and is biased downwardly by coil 403d. The upward force provided by bellow 403b against coil 403d may be controlled by adjusting its position within piston 402 by adjusting screw portion 42 of bellows element 403 received in the bottom portion of piston 402. When the pressure in cylinder 401 is less than the pressure within bellows 403b, bellows 403b expands, needle-ball type valve 41 is pushed upwardly, and opening 402a of piston 402 is opened. Therefore, discharge chamber 281 is placed in fluid communication with the interior of piston 402, no pressure builds in the space of cylinder 401 above piston 402 and piston 402 does not move downwardly, and intermediate pressure chamber 282 is linked to communication chamber 283. The compression ratio is decreased.
When the pressure in cylinder 401 is greater than the pressure within bellows 403b, bellows 403b contracts and needle-ball type valve 41 moves downwardly and obstructs opening 402a of piston 402. Discharge chamber 281 is not in fluid communication with the interior of piston 402, and the compressed fluid from discharge chamber 281 acts on the upper end surface of piston valve 402 pushing it downwardly against the recoil strength of spring 404 and sealing hole 361b. The link between communication chamber 283 and intermediate pressure chamber 282 is terminated and the compression ratio is increased.
In the embodiment of FIGS. 4 and 5, whenever bellows 403b contracts due to suction pressure and seals hole 402a, piston 402 will be moved downwardly due to the pressure of the fluid from discharge chamber 281 which builds up above piston 402. However, whenever bellows 403b expands due to lower suction pressure, fluid from the top of cylinder 401 flows through piston 402 to suction chamber 271. Piston 402 moves upwardly, allowing suction chamber 271 and intermediate pressure chamber 282 to be linked. Piston 402 will move upwardly even if at first the discharge pressure is higher than the suction pressure.
The embodiment of FIGS. 4 and 5 has the disadvantage that if compressor operation is restarted too quickly after it has been terminated, possible damage to the driving mechanism of the automobile may result. If the compressor functioning terminates during high capacity operation, piston 402 will be in its lower position due to the discharge pressure, isolating chamber 282 from chamber 283. Bellows 403b will remain contracted, sealing hole 402a until the suction pressure is dissipated sufficiently to allow hole 402a to be opened to equalize the suction and discharge pressures. Additionally, the pressure at the top of cylinder 401 linked to discharge chamber 281 will also dissipate slowly after the compressor stops operation. Thus, there will be a time delay after the stop of compressor operation before piston 402 moves upwardly and the compressor is returned to minimal capacity. If the compressor begins operating again at maximum capacity before piston 402 moves upwardly, the compressor will start operation at the maximum compression volume, damaging the driving mechanism of the automobile. Additionally, durability of the compressor will be reduced.